This invention relates to an improvement in a device for suppressing vibration of a structure such as a building, bridge and the like, the vibration being caused by a vibration source such as wind, earthquake, traffic and the like.
In recent development made in the field of high strength materials and in the rapid progress made in both construction engineering and computerized structure analysis, modern buildings and civil structures have been enlarged in scale, varied in types, and have become comparatively lightweight and flexible. As the buildings and the structures become more lightweight and more flexible, their natural frequency and vibration damping factors tend to be more lessened. Hence, there is the possibility that various kinds of vibration may unexpectedly occur in the structures due to a vibration source such as earthquake, wind, traffic and the like. In particular, as building structures are enlarged in scale, the amplitude of vibration of the structures caused by a vibration sources is enlarged. Such a large amplitude vibration of the structures is likely to give uneasiness to occupants of the building structures and also to induce excess stresses beyond an allowable level in the structures.
To eliminate the inconvenience described above, the inventor of the present invention has previously proposed, in Japanese Patent Application No. 60-241045, a device for suppressing vibration of a structure. This device has a tank disposed at a predetermined position such as the roof and the like of the structure. The tank contains such an amount of liquid that the natural period of the liquid is equal to that of the structure. When the structure is vibrated due to a vibration source, the liquid in the tank is also vibrated with the same vibration period as the structure for a quarter of a period out of phase compared to the structure, thereby suppressing the vibration of the structure.
However, since the above mentioned prior device suppresses the vibration of the structure by the liquid vibrating together with the structure, there is a possibility of the device acting adversely as a vibrator for the structure after the vibration amplitude of the structure becomes smaller than that of the liquid in the tank. Therefore, it has been required that the vibration-suppressing device should have suitable means for positively dampening the vibration of the liquid depending on the arrangement of the structure and on the scale of the device.